The metastic dissemination of tumor cells within the circulation may involve platelets in transport of tumor cell emboli and in their attachment to the vessel wall. We will utilize the Baumgartner in vitro perfusion system to measure the interaction of cultured human tumor cells and of mixed tumor cell-platelet thrombi with endothelial cells and subendothelial elements to evaluate the attachment phase and tumor cell-induced platelet aggregation to evaluate some of the factors which might affect transport in the circulation. These include the rheology of the system, role of plasma factors and of cellular elements such as lymphocytes, effects of antiaggregating drugs and prostaglandins and modification of platelet, tumor cell and endothelial cell surfaces. Blood from patients with various platelet defects such as Bernard-Soulier syndrome, Glanzmann's thrombasthenia and storage pool defect will also be examined. The interactions we will study include platelet-platelet, platelet-tumor cell, tumor cell-endothelium and subendothelium and platelet-tumor cell thrombus with the subendothelium.